Are rod bipolar cells always depolarized or hyperpolarized in the light?

Rod bipolar cells are typically depolarized in the presence of light. This phenomenon occurs as part of the pathway of phototransduction in the retina. In darkness, rod photoreceptors release the neurotransmitter glutamate, which then activates inhibitory pathways leading to the hyperpolarization of rod bipolar cells. However, when light strikes the rods, it initiates a cascade of events that ultimately results in the closure of sodium channels. This closure reduces the inner current, causing the rods to hyperpolarize and consequently decrease their release of glutamate.

As the glutamate levels drop, the inhibitory influence on the rod bipolar cells is lifted. This results in the depolarization of rod bipolar cells, as they start to become activated due to the reduced inhibition. Hence, when light is present, rod bipolar cells show a net depolarization response, which contrasts with their behavior in darkness where they are hyperpolarized due to continuous glutamate release from the rods. Through this mechanism, rod bipolar cells contribute to the process of visual signal transmission in low-light conditions, allowing for sight under these conditions.